forCodingInterviews

Question 1

if there are duplicate elements x in a list, then what does a.remove(‘x’) remove?

Answer 1

the first occurrence of x

Question 2

finding the intersection of two sets

Answer 2

result = s1.intersection(s2) s1 & s2

Question 3

finding the union of two sets

Answer 3

resul = s1.union(s2) or s1 | s2

Question 4

how to iterate over a set?

Answer 4

for val in set: print(val)

Question 5

convert a set into a list

Answer 5

list(s)

Question 6

set membership

Answer 6

if element in set

Question 7

dict membership

Answer 7

id key in d

Question 8

list membership

Answer 8

if element in list

Question 9

what does a filter function return and what’s one way to make it usable

Answer 9

it returns a filter object and can convert into list using list(filter(function, iterable))

Question 10

can you use a filter object with a set?

Answer 10

yes

Question 11

how to create a list of tuples from a dictionary such that a tuple is (key, value)?

Answer 11

list(dict.items());

Question 12

adding an element to a tuple

Answer 12

remmeber tuples are immutable so t2 = t1 + (newElement,) REMEMBER THE COMMA AT THE END. This is creating a new tuple since tuples are immutable.

Question 13

inserting element at a particular location n in a tuple

Answer 13

t3 = t2[:n] + (‘a’,) + t2[n:]

Question 14

removing an element froma particular location n in a tupel

Answer 14

t3 = t1[:n] + t1[n+1:]

Question 15

what objects pass by reference?

Answer 15

all mutable objects, i.e. list, set and dict. Non mutable objects are passed by value so any changes to those args inside the function will not be reflected outside.

Question 16

adding elements to a set

Answer 16

a.add(2)

Question 17

whats the difference between b=a and b = a[:] where a is a list

Answer 17

b=a –> any changes to a will be reflected in b
b = a[:] –> creates a copy of a so changes in a will not be reflected
for nested lists use deepcop

Question 18

what are the largest and smallest numbers in python?

Answer 18

float(‘inf’) and float(‘-inf’)

Question 19

how do you replace a char c in a string s with char d.

Answer 19

s.replace(c,d)

Question 20

what is time complexity of python sort function

Answer 20

nlogn - uses Timsort

Question 21

creating permutations (combinations) in python

Answer 21

from itertools import permutations
p = permutations(list,r)
for combination use combinations
returns a list of tuples, each containing a permutation (or combination)

Question 22

check if n is power of 2

Answer 22

n & (n-1) == 0 and n not 0

Question 23

check if power of 4

Answer 23

check for power of 2 and (n-1) % 3 == 0

Question 24

if s is a string what does sorted(s) do?

Answer 24

splits characters of s into a list and sorts it. If there are numbers they come first

Question 25

how to convert a string of 0s and 1s into a base 10 integer?

Answer 25

i = int(s,2) assuming it’s currently binary

Question 26

how to convert all chars of a string to upper case?

Answer 26

s.upper()

Question 27

how to convert all chars of a string to lower case?

Answer 27

s.lower()

Question 28

how to ascertain if all chars of a string are digits?

Answer 28

s.isdigit()

Question 29

how to convert all chars of a string are alphabets?

Answer 29

s.isalpha() will return false even if there is one space

Question 30

convert a character is ascii representation?

Answer 30

ord(char)

Question 31

convert an integer to a char using ascii representation

Answer 31

chr(int)

Question 32

convert an integer into a string representation

Answer 32

str(int)

Question 33

how to create a named tuple

Answer 33

from collections import namedtuple
Node = namedtuple(“Node”, [“key”, “value”])
new_node = Node(‘k’, 1)

Question 34

when to use == and when to use “is”

Answer 34

except when checking if a variable is None, use ==

Question 35

what is the default data types of python division operation?

Answer 35

float

Question 36

what if you want python to return result of division in integer type and not float?

Answer 36

use //

Question 37

if you want python to evaluate default arguments fresh everytime it is called, what coding pattern to use?

Answer 37

func (default  =None):
   if not default: default = desired_value

Question 38

what objects are hashable in python

Answer 38

all immutale objects specifically strings, tuples, integers. All mutable objects such as list, set and dict are not hashable.

Question 39

how to sort a list based on a function f of it’s values (rather than the value itself)

Answer 39

a.sorted(key = lambda x: f(x))

Question 40

s1 nd s2 are two sets; get their symmetric difference. elements in set s1 only or s2 only.

Answer 40

A ^ B

Question 41

python random number generator

Answer 41

randrange(a,b,step); random number will be equal step a < b. However to get random element from list use choice(list)

Question 42

create a dictionary with default value empty list

Answer 42

d = defaultdict(list)

Question 43

creating a nested default dictionary

Answer 43

defaultdict(lambda: defaultdict(list))

Question 44

create a list with cumulative sums

Answer 44

from itertools import accumulate